Lectures 11 & 12 - Coral Reefs

Question 1

Give six key points about coral reefs

Answer 1

> high diversity only matched by rainforests
60,000 identified species but suspected 423,000
Occour in oligotophic waters
3 times as productive as coastal upwellings
make up 2? of oceanic area
over / under exploited

Question 2

What are Cnidarians

Answer 2

There are what corals essentially are, they are multicelluar simple organisms that have nematocysts for predation and defence. After firing they regenerate after a few hours

Question 3

Give 6 facts on reef distribution

Answer 3

> Found between the 18oC isotherms
Tropical and equatorial (between cancer and capricorn)
Optimum water temp 23 - 25 oC
not found on western coasts as corilois gyre brings cold water into coastal region
not found by river outflows
occour in warm oceanic currents

Question 4

What is an essential relationship between two species in coral ecology

Answer 4

Endosymbiosis between algea and animal (polyp)

Question 5

Give some details on the algea in this symbotic relationship

Answer 5

Autotrophic, dinoflagellate zooanthella. Outher meber thin and leaks metabolites which benefit the coral polyp. Algea non-motie and fragile depends on the polyp for structural surport

Question 6

Could you draw a coral polpy?

Answer 6

probably

Question 7

Cross section of a polyp membrane shoulding the zooanthellea algea

Answer 7

Probably not

Question 8

What are the three ways in which a coral can reproduce

Answer 8

> Fragmentation (in storm conditions / stress)
Colony Fission
Budding

Question 9

Explain budding in corals and the three types

Answer 9

Young polyp grows out of an older one, three types:
> Longtiudinal division - divides into two smaller ones
> Transverse division - Divides horizontally to form mouth and base region
>Intratentacular budding - new one forms on oral disc of old one

Question 10

What are the pros and cons of spawning

Answer 10

Cons - mass spawning means they are vunerable to predation and can even smother corals
Pros - “swamp” predators, there are so many that some will get fertilised eggs and sperm released at the same time

Question 11

Could you draw a diagram of sexual reproduction of corals with regards to brooders and broadcasters

Answer 11

flow diagram needed here ………………………………………………………………………………………………………………………………………………………….

Question 12

What are the 8 factors effecting time of spawning (not really known)

Answer 12

> Sea Temp
> Lunar cycle (tides??)
> Day lenght
> Irradiance
> Wind and currents
> Rainfall
> Chemical stimuli
> Latitude

Question 13

Explain colony growth 4 types and explanataion

Answer 13

Colony is called a Coenorsarc
Division - gradual laying down of calcium carbonate between corallites
Stolons - root like growth that covers surface and then polyps grow out of it
Monopodal growth - growth of new polyp on older one
Sympodal Growth - young one grows on the edges
Dycotomic growth - symmetric division of polyps

Question 14

What are the four reef forms

Answer 14

Fringing
Platform
Bank
Barrier

Question 15

Explain reef zonation from shore to sea

Answer 15

Lagoon
Back reef
reef flat
reef crest
fore reef

Question 16

Explain reef zonation in terms of depth on the fore reef

Answer 16

Branching coral zone
mixed coral zone
massive coral zone
deep fore reef
platy coral zone

Question 17

Explain morphology of corals with regards to wave energy (most tollerant at the bottom)

Answer 17

Braching
Pillar
Tabular
Massive
Encrusting
Mushroom

Question 18

Zonation of coral reefs - Lagoon. Explain

Answer 18

sandy substratum, seagrass beds, e.g. Syringodium spp.- important nursery grounds for reef fish. Also benthic organisms, e.g. echinoderms - holothuroidae - sea cucumbers in high densities. Also get coral growth from fragments broken off by wave and storm damage. These small areas of coral also act as nursery grounds for reef species of fish and invertebrates.

Question 19

Zonation of coral reefs - reef back

Answer 19

Limited water movement, therefore low diversity massive corals are found here such as:
Fire coral - big time sting
Giant Clam - englufed in corals
Also get soft corals as wave energy decreases

Question 20

Reef flat explain

Answer 20

At low tide can be exposed, dominated by branching taxa, fauna found is fish, invertbrates, filametous algea. Massive diversity of fish

Question 21

Reef front explanation

Answer 21

Reef crest quite shallow, high wave action of no corals as frequently exposed, as you move down the reef front there are fast growing corals then slow growing tabular corals to low light levels, turtles and marine mammals

Question 22

Give three examples of species mutlatlism

Answer 22

> Predatory fish and cleaner fish (e.g. Labroides spp.).
Trapezia crab spp. and Alpheus pistol shrimp spp. defend their host coral Pocillopora against grazing asteroidae e.g. Acanthaster spp.
Clown fish (Amphiprion spp.) and anemones (Hetractic spp.)

Question 23

What are the main threats to coral reefs

Answer 23

Natural - grazing pressure, urchins, crown of thornes starfish
Human - coral bleaching linked to high temp of sea water, light damage, the zooxanthellae are ejected or die